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Yogurt
Milk Production Large Scale Production Milk Standarization Milk solid contents are often adjusted by mixing milk with skim milk, cream or milk powders. Milk Powders include Include non-fat dry milk, whey protein concentrates, or milk protein concentrate, can all be blended with milk. The milk solids content ranged from 9% (skim milk) to 20% (concentrate). Certain yogurt properties including texture, consistency, appearance, viscosity and the prevention of whey separation can be maintained by the use of stabilizers, such as pectin or gelatin. Homogenization Milk base is homogenized to prevent fat separation during the process of fermentation, in order to maintain the fat content within yogurt. Homogenization can improve other properties including, whey separation, yogurt consistency and appearance. Under the temperature range of 55-65°C, the standard pressure settings include: • First stage pressure: 10-20 MPa • Second stage pressure: 5 MPa • Ultra- high: 200-300 MPa · Pasteurization The milk heat treatment influences the physical properties and microstructure of yogurt. It can also destroy unwanted microbes and removed dissolved oxygen, to encourage anaerobic fermentation and improve yogurt quality. After pasteurization, bacterial cultures can be added. Few common settings for heat treatment include • 85°C for 30 min • 90-95°C for 5min • High temperature short time (100°C - 130°C for 4 - 16 s) • Ultra-heat temperature (140°C for 4 - 16 s) Fermentation After pasteurization, milk is cooled to the incubation temperature of 40°C to 45°C for the growth of thermophilic acid bacteria. The temperature decrease also allowed for the conversion of lactose to lactic acid, decreasing the pH from 6.7 to ≤ 4.6. The decrease in pH causes gelation which is one of the key steps in forming yogurt. Two thermophilic bacteria: • Streptococcus ''subsp. ''Thermophilus • Lactobacillus delbrueckii ''subsp. ''bulgaricus Cooling The cooling process continues until it reached 20°C. At this temperature, fruit or flavouring ingredients can be added. At less than 10°C, further acidification continues. After cooling, the mechanism of stirred or set yogurt branches off. Set yogurt enters the cold storage directly, reaching 10°C. Stirred yogurt has to be cooled by agitation, and then placed in cold storage. Small scale production – making it at home Home-made yogurts give rise to certain advantages of being simple, cheap, and organic with no additives/sweeteners added. Small scale production requires ingredients of 4 cups of milk and 2 tablespoons of plain yogurt with active cultured. pH and Temperature Optima Optimal growth conditions were found at pH 6.5 and 40°C for S. thermophilus and pH 5.8 and 44°C for L. bulgaricus. The pH and temperature optima of the acidification characteristics differ from those of growth: they are consistently higher by 0.1 to 0.2 pH units and by about 5 ° C, except in the case of L. bulgaricus, for which the optimal temperature is in all cases equal to 44 ° C (Beal, 1989) Facultative vs. Obligate Anaerobes Streptococcus Thermophilus is a facultative anaerobic organism. A facultative anerobe produces ATP by aerobic respiration in the presence of oxygen but is also capable of switching to fermentation. Lactobacillus bulgaricus is also a facultative anaerobic organism. Obligate anaerobes die in the presence of oxygen so they can only undergo fermentation as they cannot produce ATP by aerobic respiration.